This invention relates to a compliant leak detection system.
Considerable research and development (R&D) efforts have been exerted around the world to develop technologies to detect water leaks in water distribution networks. Water leakage can reach 30% on average of the water transported across water distribution networks [1, 2]. Current leak detection methods [3] include leak noise correlators, surface listening devices, ground penetrating radars, infrared thermography, and chemical tracing. These methods have many limitations when applied to actual water distribution networks. They can be expensive or time consuming, inaccurate, have noise interference problems, and sometimes depend on pipe material.
Acoustic and noise correlators [4, 5] are the widely used methods for leak detection at the present time by water municipalities worldwide. These methods work well in metal pipes; however, the effectiveness of the methods is doubtful with plastic pipes due to high signal attenuation, low frequency content, and the pronounced effect of fittings on the wave propagation. Recently, leak detection using in-pipe moving sensors, like Sahara and Smartball systems, is considered to overcome many shortcomings of the conventional acoustic leak detection devices. The motivation for venturing into this technique stems from the ability to survey a long distance pipeline in a network and surveying portions of the network which may be logistically difficult to access by other techniques. The closeness of the sensor to the leak location may enable capturing clean signals so leak detection and localization becomes more independent of pipe material, pipe depth, soil type, background noise, and other environmental effects.
Based on detailed computer simulations and experimental validation, leaks can be detected by local pressure measurements. However, the pressure affected region is highly localized and this method requires a large number (more than 20 for a 2 mm leak size) of pressure transducers or equivalent sensors in order to detect a leak. This situation is mainly due to the fact that the pressure gradient caused by a leak is highly localized and its effect can only be sensed 1-2 leak diameters around the leak center. FIGS. 1a, 1b and 1c show a typical result where changes in the pressure distribution caused by leak are difficult to detect along the pipe centerline. Detection is only possible in the vicinity of the leak.
Ben-Mansour et al (U.S. Pat. No. 8,869,599 B2) invented a novel method that transforms the high-pressure gradient in the vicinity of the leak position into a force and consequently into a displacement that can be sensed by a small number of transducers (strain gages, load cells, piezo-electric transducers, etc.) which are optimally located. The transformation of the suction pressure (gradient) created by the leak into a force is accomplished by the use of a rigid body (a suction drum) which is suspended by force transducers connected on one end to the rigid body and Another end to a reference point (outer cage). The benefits of reducing the number of sensors are many and most of them are obvious. These include reduction of the product cost, reliability of the sensing system, reduction of the amount of data to be processed and hence the amount of power consumed as well as of the data processing requirements.
The system described above (U.S. Pat. No. 8,869,599 B2) works very well in clean and straight pipes. However water distribution pipes are far from clean once they are in use for more than one year. Because of solid particles dissolved in water, over time the pipes get scaled. The scale content depends on the solid particles carried by water. A clean and a scaled pipe are shown in FIG. 2. Under these condition the pipe has a variable diameter as the leak detector moves.
An object of the present invention is a compliant leak detection system that has the capability to change its outer size so as to bring a detecting structure such as a membrane close to a pipe (scaled or clean) wall at all times to detect a leak.